DE3242444C2 - Process for the production of a grain-oriented electrical steel sheet - Google Patents

Abstract

In a new method, a desired texture can be formed by a specified heating of a steel strip prior to performing cold rolling and at the same time the breakage of the cold rolled strip can be prevented. Before cold rolling, the strip is heated to a temperature in a range between the minimum temperature, which is at least 200 ° C and furthermore at least T ↓ L (° C) = (x-3.0) ↑ 2 100, where x is the silicon content is in percent by weight, and the maximum temperature, which does not exceed 400 ° C and at most T ↓ H (° C) = -200 log (↑ 1 / ↓ y), where y is the deformation rate (s ↑ - ↑ 1) during cold rolling is, so that the temperature during the first pass of cold rolling is appropriately determined.

Description

- both the minimum temperature, which is at least 200 ° C and at least equal to T ₁ (° C) = (x-3.0) ² -100, where χ is the silica content in percent by weight,

- as well as the maximum temperature, which is not more than 400 ° C and at most equal to T "(° C) = - 200 · log (J-), where y is the strain rate (seconds - ') during cold rolling,

be determined so that the temperature is maintained in the first pass of cold rolling.

2. The method according to claim 1, characterized in that the SÜicIumhalt of 3 wt-96 to 4.5% by weight is -96.

3. The method according to claim 1 or 2, characterized in that the second and the following Passes of cold rolling can be carried out without intentionally heating the steel strip.

4. The method according to any one of claims 1 to 3, characterized in that the silicon steel of 0.010 contains up to 0.065% by weight of acid-soluble aluminum.

5. The method according to any one of claims 1 to 4, characterized in that the decrease in thickness of 81 to 95%.

6. The method according to any one of claims 1 to 4, characterized in that the annealing temperature of 950 ° C to 1200 ° C.

The present invention relates to a method for producing a grain-oriented electrical steel sheet, which has a high magnetic flux density and a low magnetic reversal loss (watt loss). In particular, the invention relates to a method in which the production conditions are optimized so that a breakage of the steel band due to embrittlement is avoided and excellent magnetic properties, d. H. a high magnetic flux density and low core losses can be obtained can.

Usually, grain-oriented electrical steel sheets are produced by a process that follows the successive Steps of hot rolling, annealing, cold rolling, decarburization annealing and finishing high temperature annealing includes.

The texture is the dominant factor that determines the magnetic properties of an electrical steel sheet product certainly. Especially when the texture of a band of Sillctum steel has a preferred orientation in the [001] direction, i. H. the direction of the easiest magnetization of an Elsenkrystal is parallel A grain-oriented electrical steel sheet with excellent magnetic properties are produced. The texture of the grain oriented steel sheet becomes generated during the second recrystallization which occurs during the final high temperature anneal.

The secondary recrystallization is caused by the processing conditions in the decarburization annealing and influenced during cold rolling. One of the fundamental factors responsible for the occurrence of secondary recrystallization is responsible for the formation of the texture due to sliding deformation during cold rolling of the Steel belt. The type of sliding twist determines the types and lifespan of potential secondary Recrystallization nuclei that appear in the primary recrystallization texture as a result of the decarburization annealing are formed.

The magnetic properties of silicon steel can be improved by increasing the silicon content can be improved considerably. An increase in the silicon content advantageously leads to a Increase in electrical resistivity, which in turn leads to a decrease in eddy currents and leads to a decrease in magnetic reversal losses (watt losses). An increase in the silicon content is however, usually accompanied by embrittlement and aggravation of cold rolling operation. the Embrittlement of silicon steel during the cold rolling process takes place on the way of separating fracture, the one The result of twinning within a relatively low temperature range, and the blue crumpling, the consequence of aging as a result of dynamic deformation in a high temperature range.

It is well known that the break point in silicon steel becomes very likely when the silicon content high and the deformation temperature is low. One could therefore very easily develop the idea of a silicon steel subject to high temperature rolling in order to report a separation fracture.

Japanese Patent Publication No. 47-39 448 (October 5, 1972) discloses a method of prevention the brittleness of a silicon steel used as an Elektro-B'-ech. In this process, alloying Elements such as Ca, Mg, Zr, Tl, V and W are added to the steel.

It is for a silicon steel used as an electrical sheet, particularly a silicon steel used as a A grain oriented steel sheet is used, not just the processing adaptability

to improve, but also to improve the magnetic properties.

Since, as described above, the texture of the steel strip is the dominant factor that affects the magnetic Properties determined, the manufacturing steps must be particularly taken into account, the In more advantageous Wise control of texture rather than being able to primarily improve manufacturing adaptability. So can therefore, even if the usual Kdt rolling is replaced by the so-called hot rolling, which at at a rather high temperature, a desired texture will not be formed.

This is easy to understand if you look at the technical developments in the manufacture of electrical sheet metal taken into account up to the present point in time. In the early days, electrical sheets were of high quality hot rolled sheets containing about 4.5% silicon.

These hot-rolled Elektio sheets were improved in adaptation to the requirements for magnetic Properties replaced by cold-rolled sheets. These requirements were mainly thereby fulfilled that one controlled the texture of the steel belt. In addition, the silicon content was about 4.5% about a maximum of 3% lower, the last value representing the silicon content of modern electrical sheets.

The background to the present invention will now be further explained in metallurgical terms. The effective slip planes of a silicon steel change depending on the temperature during the cold rolling step to achieve a final thickness. The number of crystal planes is at a low one Rolling temperature is limited, which is why the plastic deformation during cold rolling is not due to sliding deformation can be caught. A twin deformation must therefore be induced, and a twin deformation can lead to a break.

When the temperature in the rolling step is high, the number of effective sliding planes of a silicon steel becomes increases, with the result that the type of crystal orientation is undesirably changed. Leading leads to undesirable changes in the primary recrystallization texture and causes incomplete secondary recrystallization or an undesirable change in the preferred orientation in the secondary Recrystallization. This leads to the fact that the magnetic properties of a grain-oriented Elect> O steel sheet and hence it is impossible to simply use the ordinary cold rolling method to be replaced by hot rolling.

It is known to control the texture of an extra-what steel sheet for deep drawing by that one carries out hot rolling. However, since the preferred orientation of an extra-which steel sheet is completely differs from that of an electric sheet, the known hot rolling can in no way be used for this purpose be able to control the texture of an electrical plate where the purpose of controlling the texture is to in particular to increase the magnetic flux density.

Incidentally, the hot rolling of steel was taboo because of its blue fragility.

It is therefore an object of the present invention to provide a method which allows, in combination together

- a high magnetic flux density primarily through the creation of a desirable texture and secondly through a high silicon content,

- to achieve low magnetic reversal losses through a high silicon content and on the other hand

- To prevent embrittlement as a result of separating fracture and blue brittleness due to the high silicon content.

This object is achieved in a method for producing a grain-oriented electrical steel sheet having a high magnetic flux density and low magnetic reversal losses, in which a silicon steel containing from 3.0 to 5.0% by weight of silicon and not more than 0.085% by weight Contains carbon, hot rolled one after the other, ^{annealed in a temperature range from 850 to 1200 0} C, preferably from 950 to 1200 ⁰ C and then rapidly cooled, then with a thickness decrease of 7696 to 95%, preferably from 81% to 9596 to final sheet metal sheets is cold-rolled, and then subjected to a decarburization annealing and a final high-temperature annealing, achieved according to the invention in that the steel strip is preheated to a temperature in a temperature range before the cold rolling is carried out

- both the minimum temperature, which is at least 200 ° C and at least equal to T ^ (° C) = (x - 3.0) ² χ 100, where χ is the silicon content in% by weight,

- as well as the maximum temperature, which is not more than 400 ° C and at most equal to T _w (° O = - 200 ■ log (1), where y is the forming speed (seconds " ¹ ) during cold rolling, ^

be determined so that this temperature is maintained during the first cold rolling pass. The process according to the invention comprises the following stages in the order given:

- Hot rolling of a silicon steel containing from 3.0 to 5.0% by weight of silicon and not more than 0.085% by weight Contains carbon;

- Annealing the hot-rolled strip at a temperature of 850 to 1200 ° C, preferably from 950 to 1200 C. and subsequent rapid cooling;

- Heating the annealed strip to a temperature in a temperature range through which both the minimum temperature, at least 200 ° C and at least gidch T _t (° C) = (x - 3.0) ² · 100, where χ is the silicon content in % By weight, and the maximum temperature which is not more than 400 ° C and at most equal to T "(° C) = - 200 · log ψ, where y is the deformation rate (seconds ^-1 ) during cold rolling

f is set so that the temperature is maintained in the first pass of cold rolling;

- Cold rolling the preheated strip with a thickness reduction of 76% to 95%, preferably from 81% to

95%;

Decarburization annealing of the cold rolled strip; and

- Final high temperature annealing of the decarburization annealed strip.

The following explains the difficulties encountered in developing the cold rolling process according to the invention had to be overcome.

It is easy to make the determination that what is needed to create the texture is the smoothing mechanism suitable to control during cold rolling. The occurrence of sliding rotation of the Crystals during rolling, however, is mainly a theory, which is why a concrete and reliable technlk to create the desired texture in a steel strip, through which the magnetic flux thickness is improved, cannot be developed based on it.

It was therefore found in the development of the method according to the invention that it is necessary To study the microstructure of a cold rolled strip in detail and therefore the microstructures of such a tape using electron microscopy with a view to forming the texture Investigated in an elaborate manner.

The two figures show the results of such an electron microscopic examination. Flg. 1 (a) Is an electron micrograph of a thin section with the structure of a kaitgewaizten Silicon steel band. The type of microstructure shown becomes a desirable orientation in End product.

Fig. 1 (b) is an electron micrograph of a thin section similar to that of Fig. 1 (a). Of the However, the type of microstructure shown here results in an undesirable orientation of the end product.

As a result of the extensive investigations it was found that to create a grain-oriented Electrical steel sheet with a desired orientation, the dislocation groups that occur during cold rolling must be linearly arranged in the cold-rolled slilclum steel sheet.

Such a linear arrangement of the dislocation groups is shown in FIG. 1 (a) shown at 1000X magnification. The cold-rolled strip according to Flg. 1 (a) was produced by a method in which a silicon steel containing 0.04% by weight of carbon, 4.0% by weight of silicon and 0.03% by weight of acid-soluble aluminum was first hot-rolled, see above that a 2.3 mm thick hot rolled strip was obtained. Thereafter, the hot-rolled strip was continuously annealed at 1150 ° C, then rapidly cooled and heated to 25O ⁰ C. The hot strip treated in this way was then introduced into the first pass of cold rolling at a temperature of 250 ° C. at a deformation rate of 8 × 10 ^-3 r ¹ . The obtained cold-rolled strip had dislocation groups which were generated during cold-rolling and which had a linear arrangement.

When the strip had been subjected to the remaining cold rolling passes at 250 ^° C. and the final high temperature annealing, a final product was obtained which showed the following magnetic properties:

B ₈ = 1.94 T and P 1.7 = 1.06 W / kg.

The same process that was used to produce the steel strip shown in FIG. 1 (a) was also used to produce the steel strip shown in FIG. 1 (b) was applied, with the difference that the steel strip was heated to a temperature of 450 ° C instead of 250 ° C before cold rolling. The dislocation groups in the obtained cold-rolled strip were randomly arranged so that the desired magnetic properties could not be obtained.
In creating the present invention, extensive studies were carried out in the fields of steel chemistry, heat treatment and the WaIz process for a steel strip in order to determine which of the stated factors is necessary for the formation of the microstructure of the steel strip, for example for the Structure shown in Flg. 1 (a). As a result of these investigations, it was found that if a silicon steel is heated to a temperature of 200 ° C to 400 ° C before cold rolling so that the carbon is sufficiently retained in the solid state, this dissolved carbon causes the movement of dislocation groups hindered during cold rolling, with the result that a linear arrangement of dislocation groups can be obtained.

The Aufneiztemperaiui before performing the Kak rolling must therefore in the range of 200 ° C to 400 ° C and soaking should be done for at least 3 minutes to be satisfactory to keep the carbon dissolved. When the preheating temperature exceeds 400 ° C, the carbon shows the Tendency to precipitate in the form of carbides, which somewhat disrupt the linear arrangement of the dislocation groups.

If the movement of the dislocation groups is hindered so drastically that aging is completely induced after dynamic deformation, steel embrittlement occurs, that is, blue brittleness occurs, and the steel strip breaks in the cold rolling step. Although it is known to control the preheating temperature so that the blue brittleness is prevented, the inventors found that, in addition to the rolling temperature, the forming speed is also an important factor in preventing blue brittleness. In making the present invention, the steel chemistry and rolling conditions for a steel strip have also been extensively studied to determine which factors determine the critical conditions at which blue brittleness will occur. As a result of the investigations it was found that the maximum preheating temperature T _w (° C) of the steel strip must be - 200 · \ og (-) ,

where y is the deformation speed (seconds " ¹ ). ^y

That is, even if the preheating temperature is in a range from 200 ° C. to 400 ° C., blue brittleness occurs when a temperature exceeding the maximum temperature T _{H is applied.} In addition, it has been found that the minimum temperatures are determined on the basis of the silicon content

got to. If the temperature is lower than the minimum preheating temperature, rolling becomes impossible even if the preheating temperature is in the range of 200 ° C to 400 ° C. Therefore, the minimum preheating temperature T _t (° C) must have the value of (x - 3, O) ² · 100 ° C, where χ is the silicon content in weight-96. When the silicon content exceeds 596, a silicon steel becomes brittle at a temperature of 400 ° C or less. In such a case, not only is it impossible to prevent breakage of the steel strip during cold rolling, but it is also impossible to control the texture of the steel strip so as to achieve the effects of the present invention. The maximum silicon content must therefore be 596. When the silicon content is 3.0% or more, the formula (x - 3.0) ² x 100 shows that there is a danger of embrittlement during cold rolling at room temperature. However, embrittlement can be prevented by adjusting the preheating temperature to the value of T _t or higher. The minimum silicon content can be 3.096. Preferably ranges for the silicon content are between 396 to 4.596. When acid-soluble aluminum is used as the inhibitor, its content is preferably in the range of 0.010% by weight to 0.065% by weight.

Since it is possible to carry out the first pass of cold rolling using a silicon-relchen steel, because the maximum and minimum preheating temperatures for preheating before the first cold rolling pass are restricted in the manner indicated, may according to the present invention in the cold rolling step a desired texture can be obtained, and at the same time, breakage due to embrittlement can occur be prevented. The second and subsequent Kaitwaiz passes can be done without any intentional Heating of the steel strip, because at this point the linearly arranged dislocation groups, which are generated during the execution of the first cold rolling pass, a separating fracture prevented if the second and subsequent Kaitwaiz passes are carried out. That means that the natural cooling during cold rolling does not pose any problems.

In addition, the heat generated by the plastic deformation becomes the final temperature of cold rolling usually held at a temperature in the range from 180 to 350 ° C.

Although the term "cold rolling" is used above, cold rolling according to the invention differs essentially in that, according to the present invention, the rolling temperature of a conventional cold rolling during the first cold rolling pass is controlled by the silicon content and the forming speed must be taken into account. Furthermore, that during ordinary cold rolling is also different The working heat generated is largely dependent on the heat to which a silicon steel is exposed before the cold rolling stage, since only the last-mentioned heat can lead to the generation of linearly arranged dislocation groups [Fig. 1 (a)] when performing the first pass of cold rolling.

Furthermore, the present invention differs significantly from a known method, as it is in the DE-AS 24 29 237 is described.

In this known method, a silicon steel is produced between the cold rolling passes from the above reasons described kept within a predetermined temperature range. According to the present In accordance with the invention, the reduction in thickness of the steel strip during cold rolling is in the range from 7696 to 9596, preferably from 8196 to 9596 since such a large decrease in thickness to form a desired texture contributes. The cold rolling can be carried out using conventional reversible cold rolling mill equipment and a Heating device, such as an oil bath, can be carried out, which is used to keep the steel belt to be heated before cold rolling.

The hot rolling stage, the decarburization annealing stage and the final high temperature annealing stage can be in one to usual manner.

The invention is explained in more detail below with the aid of exemplary embodiments.

example 1

Silicon steels having the compositions shown in Table 1 were continuously cast into slabs, and thereafter the slabs were hot-rolled so that 2.3 mm thick hot-rolled strips were obtained. The hot-rolled strips have been continuously annealed at 115o C ^0, after which they were rapidly cooled, and then a cold rolling passages Kaitwaiz comprised 10 by a reversible system, performed.

In this process, the hot rolled strips were subjected to one of the following treatments: direct cold rolling; Heating to 150 ° C for 20 minutes; Heating to 300 ^° C. for 20 minutes; Heating to 450 ° C for 20 minutes; then the hot-rolled strips, which were heated in the specified manner, were directly cold-rolled. Therefore, the temperatures in the first cold rolling pass were either room temperature or 150 ° C., 300 ° C. or 450 ° C. The forming speed during the first cold rolling pass was 3/4 " ³ seconds" ¹ .

The obtained 0.27 mm thick cold-rolled strips, which were formed with a thickness reduction of 8796, were subjected to decarburization annealing at 850 ° C and then finishing high-temperature annealing at 1200 ° C subjected.

■ «if
W.

30th

35

40

45

50

55

60

65

Table 1

Steels

Wt%

Si wt%

Mn
Wt%

Weight- «/

A. B. C. D. E.

0.05
0.05
0.06
0.06
0.06

2.85 3.32 3.88 4.55 5.10

0.09
0.09
0.09
0.08
0.08

0.03
0.03
0.03
0.03
0.02

acid-
soluble
Al
% By weight N
Wt% 0.03 0.007 0.03 0.007 0.03 0.007 0.03 0.006 0.03 0.007

The results of secondary recrystallization, the magnetic properties of the end products and the Occurrence of spraying during the Kaltwa'.z step are summarized in Table 2.

Table 2

Steels

Temperature at room temperature 1st cold rolling (comparative example) pass

150 ° C

300 ° C

450 ° C

A.

Incomplete

secondary

Recrystallization

Incomplete secondary recrystallization. Breakage in the 1st cold rolling pass

Breakage in the 1st cold rolling pass

E break at

(Comparative example) 1st cold rolling pass

B ₈ in Tesia (T): P 1.7 in ω / kg

B ₈ = 1.85

P 1.7 = 1.15

B ₈ = 1.85
P 1.7 = 1.14

B ₈ = 1.84
P 1.7 = 1.15

Break at
2nd cold rolling pass

Break at
2. Potash pass

B ₈ = 1.92 P 1.7 = 1.12

B ₈ = 1.92 P 1.7 = 1.08

B ₈ = 1.91 P 1.7 = 1.06

B = 1.91
P 1.7 = 1.05

Breakage during the 2nd pass of potash

Incomplete secondary recrystallization (comparative example)

B ₈ <1.8

t <1.8

Incomplete secondary recrystallization (comparative example)

Incomplete secondary recrystallization (comparative example)

As shown in Table 2, the secondary recrystallization was complete and none occurred during cold rolling Breakage due to embrittlement, except in the specified cases.

In the case of steel D, the minimum preheating temperature T _{L was} (4.55-3.0) ² · 100-, which gives a value of 240 ° C. The temperature in the first cold rolling pass was 150 ^° C. and was therefore too low to prevent embrittlement.

For this reason, since the maximum preheating temperature T _{w was} 600 ° C, the strain rate was very low, ie 10 ^-3 seconds " ¹ , which resulted in the highest temperature of the first cold rolling pass, ie 450 ° C, being considerable was lower than the maximum preheating temperature T _w , i.e. 600 ° C.

As can be seen in Table 2, by properly controlling the temperature in the first pass of cold rolling based on the silicon content, excellent magnetic properties, ie, B ₈ = 1.9 T ₂ and P 1.7 = 1.10 watts / kg, are obtained without any undesirable incidents occurring during cold rolling.

Example 2

Using steels B and D, the procedure of Example 1 was repeated. There were however, the temperatures of the first pass of cold rolling and the strain rate varied as shown in FIG Table 3 shown to determine the occurrence of blue brittleness.

stole 32 42 444 200 S- ' • 2000 S- ' Table 3 B. Rolling is Rolling is D. possible possible temperature Deformation speed y 250 ° C B. 20 s- ' Rolling is Rolling is Considerably possible possible D. hardened 35O ⁰ C B. Rolling is difficult Rolling is Rolling is Break at difficult possible second 450 ⁰ C Passage Break at first Passage

As can be seen from the above, a method is created according to the invention that differs from the known and has considerable advantages. Common catfish is the level of calcium in one The steel used for the production of grain-oriented electrical steel sheets is a maximum of 396, since cold rolling 25 difficult when the silicon content is high. Although a common hot rolling, the poor workability of a silicon steel with a high silicon content, it was previously impossible to improve the To control the texture of a cold-rolled strip while completely preventing embrittlement. These apparently exclusive requirements, which also include excellent magnetic properties, are simultaneously satisfied by the method according to the invention. 30th

1 sheet of drawings

50

65

Claims (1)

Patent claims: 1. A method for producing a grain-oriented electrical steel sheet with a high magnetic strength Flux density and low magnetic dissipation loss with a silicon steel ranging from 3.0 to Contains 5.0 96 wt. Silicon and not more than 0.085 wt. 96 wt. Carbon, successively hot rolled into annealed in a temperature range of 850 to 1200 ° C and then rapidly cooled, then at a Thickness decrease from 76 to 9596 is cold rolled to final thickness and then a decarburization annealing and is subjected to a final high-temperature annealing, characterized in that the steel strip preheated to a temperature in a temperature range prior to performing cold rolling becomes, through the